Landing gear are well known in the art for abating structural damage to the adjoining aircraft structure, i.e., fuselage structure. Common varieties of landing gear include energy absorbing and skid landing gear types wherein energy absorbing landing gears dissipate a large portion of the aircraft's inertial energy upon ground contact and wherein skid landing gears transfer load directly into the structural members of the fuselage, i.e., bulkheads, longerons and stringers, such that energy is dissipated via elastic deformation of the skid landing gear and the adjoining fuselage structure. Energy absorbing landing gear typically comprise a complex assemblage of moving parts including a telescoping damping strut (commonly referred to as an oleo strut), which dissipates energy by shuttling fluid through a damping orifice as the landing gear is exercised, i.e., upon ground contact. Skid landing gear typically include a simple framework of tubular members or rails, which are hard mounted to the fuselage structure and which serve as a simple contact surface for arresting the motion of and supporting the aircraft upon landing.
Within the family of skid landing gear are tail skids which are mounted to the undercarriage of the aircraft's tail section to protect the same in the event of incidental contact. Tail skids typically comprise a simple beam member which is cantilever mounted to the tail section and which functions as a conventional bumper assembly.
Common applications for landing gear and/or tail skids include the tail pylon of rotorcraft, which may require support and/or protection due to the attendant weight of the overhead tail rotor/gearbox assembly and the inherent vulnerability of the tail pylon to ground strikes. With regard to the latter, the landing gear/tail skid protects the tail pylon upon landing, and, more importantly, during flared, i.e., nose-up, landing approaches wherein the tail pylon is proximal to the landing surface.
Depending upon the anticipated mission of the rotorcraft, the size, and consequently, the weight of the tail pylon and/or associated landing gear may vary significantly. For example, military rotorcraft may require structural augmentation of the tail pylon, and/or the use of a high durability landing gear to withstand landing maneuvers on rough, unprepared terrain, or survive in a more aggressive operating environment, e.g., battlefield maneuvers. Generally, energy absorbing landing gear are employed in such applications to mitigate the potential damaging effects of the anticipated high impact loads. Such energy absorbing landing gear provide a full range of protection and are designed for repetitive use.
Civil rotorcraft, on the other hand, operate in a more benign environment, and may not require structural augmentation to withstand the anticipated (lower) impact loads. Skid landing gear/tail skids may be utilized for such applications, insofar as the fuselage structure itself may be suitably designed to withstand such impact loads. Generally, skid landing gear/tail skids provide a marginal level of protection insofar as the need, i.e., mission, does not require the level of protection afforded by energy absorbing landing gear.
While it is desirable to design the tail pylon and its associated landing gear/tail skid to meet specific mission requirements, e.g., for optimizing weight, fuel efficiency and handling qualities, the practicalities of manufacturing several variants of the same aircraft configuration necessitate that certain compromises be made. By producing variants with slightly altered thickness dimensions to strengthen or lighten the structure, the manufacturer incurs additional costs associated with non-recurring engineering, tooling expenses, increased inventory, and consequently, increased overhead expenses. If the burden of such costs are not outweighed by the benefits of improved aircraft performance, or if the customer is unwilling to pay a higher price, then a decision is made to target a specific mission requirement. Typically, the design which satisfies the greatest number of requirements and largest customer base, is selected. Accordingly, the design is optimum for one select group of customers and non-optimum for all others.
A need therefore exists to provide a landing gear/tail skid which satisfies a wide spectrum of mission requirements thereby appealing to a s broader customer base.